1. Field of the Invention
The invention relates to an X-ray examination apparatus which includes
an X-ray source, PA1 an X-ray detector, PA1 an X-ray filter which includes a plurality of filter elements and is arranged between the X-ray source and the X-ray detector, PA1 an electric voltage source and a control system for selectively applying electric voltages to individual filter elements, PA1 which control system includes voltage lines, and PA1 the filter elements are formed by spaces between plates which are locally attached to one another, and PA1 the voltage lines are provided at least partly on one or more of the plates.
the filter elements being connected to the electric voltage source by way of voltage lines, and PA2 the X-ray absorptivity of the individual filter elements being adjustable by adjustment of a quantity of X-ray absorbing liquid in individual filter elements on the basis of the electric voltages applied to the individual filter elements.
2. Description of Related Art
An X-ray examination apparatus of this kind is known from international patent application WO 97/03449.
The X-ray examination apparatus is used to form an X-ray image of an object to be examined, for example a patient to be radiologically examined. The X-ray source irradiates the object by means of an X-ray beam and an X-ray image is formed on the X-ray detector due to local differences in the X-ray absorption within the object. The X-ray filter ensures that the range of brightness values of the X-ray image remains limited. The X-ray filter is adjusted in such a manner that on the one hand parts of the X-ray beam which are only insignificantly attenuated by the object are slightly attenuated by the X-ray filter and that, on the other hand, parts of the X-ray beam which are significantly attenuated by the object are transmitted by the X-ray filter practically without attenuation. Because the brightness values of the X-ray image lie within a limited range, the X-ray image can be very readily processed further in order to achieve a good rendition of even small details of low contrast.
The X-ray filter of the known X-ray examination apparatus is provided with a bundle consisting of a very large number of capillary tubes, each of which communicates with the X-ray absorbing liquid by way of one end. The quantity of X-ray absorbing liquid present in the individual capillary tubes is influenced by the electric voltage applied to the wall of the capillary tubes. It has been found that the adhesion between the wall of the capillary tubes and the X-ray absorbing liquid is dependent on the electric potential difference between the wall of such a capillary tube and the X-ray absorbing liquid.
The voltage lines extend between the capillary tubes in the X-ray filter of the known X-ray examination apparatus. The capillary tubes are connected to one of the voltage lines by way of a respective field effect transistor. The field effect transistors are arranged between the capillary tubes. It is a drawback of the X-ray filter of the known X-ray examination apparatus that a rather large amount of space is required for the voltage lines to extend between the capillary tubes. Consequently, the active surface area of the known X-ray filter is significantly smaller than the overall surface area of the X-ray filter. Moreover, the field effect transistors are arranged in a region which is exposed to X-rays during operation of the X-ray examination apparatus. The X-rays may affect the field effect transistors so that the service life of the known X-ray filter is limited.
Citation of a reference herein, or throughout this specification, is not to construed as an admission that such reference is prior art to the Applicant's invention of the invention subsequently claimed.